Abstract [en] : This licentiate thesis treats the solar wind interaction with the martian atmosphere and the water related features known as gullies, as well as some ethical issues related to the human exploration of Mars. The composition of the escaping plasma at Mars has been investigated in an analysis of data from the IMA sensor, which is part of the ASPERA-3 instrument suit onboard the European satellite Mars Express. The cause for the investigation is to determine if there are any large abundances of escaping ion species incorporating carbon, such as in CO_2^+. The most abundant ion species was found to be O^+ and O_2^+, followed by CO_2^+. The following ratios were identified: (CO_2^+)/(O^+)=0.2 and (O_2^+)/(O^+)=0.9. The loss of CO_2^+ was estimated to 4.0x10^(24) s^(-1) (0.29 kg/s). The escaping plasma in form of ion beam events has also been correlated to the magnetic anomalies found on the surface, where no clear association was found. This study is important in order to understand the evolution of Mars, since some evidence reveals that ancient Mars was once a wetter planet. The gully formations have been investigated with data from the MOC and MOLA instruments onboard the satellite Mars Global Surveyor. The intriguing features suggest that there has been fluvial erosion on the surface of Mars. The shallow and deep aquifer models remain the most plausible formation theories. Gully formation is another important piece to the puzzle regarding the lost water on Mars. Since Mars once harbored stable water on the surface in the past, astrobiologists believe that life could have existed on Mars. Some even argue for a slight possibility to find life thriving in the subsurface today, where the water can be found in a stable liquid form. If this would be the case we need to consider whether we should continue with our in-situ exploration of the surface, or if we should leave Mars to the Martians.